This invention is directd to an electronic timepiece, and in particular to a quartz crystal electronic timepiece wherein the division ratio of the divider circuit is automatically regulated in response to an external reference signal.
In prior art quartz crystal electronic timepieces, adjustment of the oscillating frequency was effected by tuning the quartz crystal oscillator circuit to regulate the accuracy of the timekeeping signals produced by the divider circuit. Such tuning was usually accomplished by changing or varying the capacitance of a trimmer capacitor in the oscillator circuit. Nevertheless, it was found that such trimmer capacitors were less then completely satisfactory because of the movable parts thereof. Moreover, because the small size of an electronic wristwatch requires the components of the timekeeping circuit to be of a miniature size, the range of capacitance was of necessity, limited, thereby considerably limiting the range over which the oscillating circuit could be tuned. Additionally, the mechanical movement required to adjust the capacitor and hence tune the oscillator circuit could not be done without experiencing considerable difficulty.
The popularity of quartz crystal electronic wristwatches, has rendered the use of inexpensive quartz crystal vibrators particularly desirable, in view of the savings provided thereby, as well as the stable operation which same affords. Accordingly, division ratio regulation circuits have been developed to regulate the division ratio of the divider circuit to produce an accurate timekeeping signal in response to an advanced or retarded high frequency timekeeping signal produced by a quartz crystal oscillator circuit. However, in the division ratio regulating circuits heretofore proposed, the number of input terminals required to establish a division ratio regulating quantity have increased, thereby increasing the size of the electronic wristwatch including same. Additionally, although such multi-terminal division ratio regulating circuits have lowered the cost of such electronic wristwatches utilizing same, the complicated nature of the circuitry utilized to provide the necessary regulation proved to be less than completely satisfactory.